1. Field of the Invention
The present invention relates to an improved treatment of epoxidate such as that formed in the commercial propylene oxide / styrene monomer process whereby the amount of water employed in the treatment is substantially reduced, and the waste material which is formed and which must be disposed of is also substantially reduced.
2. Description of the Prior Art
An extremely successful process for the co-production of propylene oxide and styrene monomer involves the molecular oxygen oxidation of ethyl benzene to form ethyl benzene hydroperoxide, the catalytic reaction of the hydroperoxide with propylene to form propylene oxide and 1-phenyl ethanol, and the dehydration of the 1-phenyl ethanol to styrene monomer. The basic patent describing this process is U.S. Pat. No. 3,351,635.
It is known to treat the epoxidate mixture, usually after separation of unreacted propylene, with aqueous sodium hydroxide. This treatment accomplishes neutralization of acidic materials, removal of soluble molybdenum catalyst and removal of phenols contained in the epoxidate. The neutralization of acidic materials is important in reducing corrosion problems which otherwise would be encountered in subsequent processing steps as well as in reducing product yield loss during subsequent distillations. The separation of catalyst is, of course, necessary, while the separation of phenols is important with regard to styrene monomer product quality and to avoid yield losses during the dehydration of 1-phenyl ethanol. Frequently, product styrene monomer is also treated with caustic in order to separate phenol which cannot readily be separated by distillation.
There are, however, problems associated with epoxidate treatment with aqueous caustic. At the high pH necessary for effective phenol removal, usually above 12, there is a significant epoxide yield loss as well as emulsification problems in decantation and problems of sodium carry over. Also, the disposal of large amounts of spent caustic solution represents a severe problem.
U.S. Pat. No. 3,439,001 shows treatment of recycle ethyl benzene with aqueous alkali in a propylene oxide / styrene monomer process.
U.S. Pat. No. 4,975,266 shows removal of phenol from 1-phenyl ethanol prior to oxidation to form hydrogen peroxide by treatment with basic anion exchange resins.
Japanese Patent Publication 56-39025 shows removing phenols from organic compounds by contact with polyvinyl pyridine resin.
U.K. Patent 1,232,710 shows the treatment of isobutane oxidate with aqueous alkali metal hydroxide or carbonate.